JPH0315629B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved process for producing methyl mercaptan from a gaseous mixture of at least one carbon oxide, hydrogen sulfide and hydrogen. According to the invention, methyl mercaptan can be obtained with a significantly higher productivity per hour compared to the productivity achieved by processes using known technology. Methyl mercaptan is of industrial interest as a major raw material for the production of various agriculturally and arable compounds, and efforts are being made to produce it as economically as possible. Many publications have published methods for heating gases containing carbon monoxide and/or carbon dioxide, hydrogen sulfide and hydrogen in the presence of catalysts based on heavy metal sulfides; This is extremely interesting considering that this raw material compound is actually inexpensive. However, since the volumetric flow rate of gas is large and the conversion rate of carbon oxides is extremely low, at low gas flow rates,
If this method were to be implemented, the productivity of methyl mercaptan would be significantly reduced. That is, U.S. Pat. No. 4,410,731, No. 4
According to the table and Table 5, the volumetric flow rate of CO or CO ₂ is 5/. At low h, the yield based on CO is 89% and the yield based on CO ₂ is 49%. The flow rate is 60/. h, the yield on a CO basis is
Does not exceed 61%, and does not exceed 24% on a _CO2 basis. Flow rate 180/. h, the yield on a CO basis is 49
%. (In Anglo-Saxon literature,
It should be noted that conversion is used interchangeably with yield, or production rate "rendement" in France. ) According to Tables 2 and 3 of European Patent No. 104507, also issued, the gas volumetric flow rate
148 and 45/. h, the yield is 21% ~
Varies between 40%. Therefore, in the case of an industrial scale, for example, column 6, section 1 of the above-mentioned U.S. patent
It is necessary to circulate the unreacted gas, as suggested in lines ~3. However, in such cases, it has been found that circulating the unreacted gas reduces the conversion even further than the result of a single pass over the catalyst as described in the literature. In order to overcome the weaknesses of the known methods mentioned above,
Until now only attempts have been made to find more suitable catalysts. Thus, according to U.S. Pat. No. 3,070,632, the addition of amines to metal sulfide catalysts is proposed, and according to U.S. Pat. European Patent No. 104507 proposes the use of manganese sulfide. However, in all these cases no consideration is given to improving the reuse of the recycled gas. The reuse of this circulating gas is the objective to be solved by the present invention. The object of the present invention is to solve the following problem: The difficulty in reusing unreacted gas is due to the fact that the reaction is inhibited by water contained in the gas after it has first passed over the catalyst. The problem was solved by finding that By removing this water, recycled gas can be used and excellent yields can be obtained. According to a first aspect of the invention, an improved method for producing methyl mercaptan from a gaseous mixture of CO and/or CO ₂ , H ₂ S and H ₂ over a metal sulfide catalyst and recycling the residual gas is characterized in that water contained in the gas is removed from the gas to be circulated after the catalytic reaction with the catalyst. This improved process according to the invention consists in drying the residual gas after separation of the mercaptan product before passing it again over the catalyst. According to a preferred embodiment of the invention, the second pass of the gas over the catalyst, and even possibly a greater number of passes, is carried out at an increased volumetric flow rate, in particular from 50 to 2000 per hour per catalyst, and more Preferably 500-1800/. It is done in h. As in known technology, the volumetric gas flow rate refers to CO, CO2 or _CO + _CO2 passing through the reactor, without taking into account other gases present, in particular _H2S and _H2 .
The target is The method of the present invention achieves a CO
and/or at a ratio of _CO2 to _H2S to _H2 , i.e., about 1/3/2 to 1/8/8. However, the method of the invention, as generally found to be used in the case of conventional methods,
Advantageously, large excesses of hydrogen sulfide and hydrogen are not required; a ratio of about 1/3/3 to 1/4/6, preferably close to 1/4/4, is sufficient. A further important advantage of the present invention lies in the fact that the utilization of carbon dioxide is significantly improved, making it possible to significantly increase the yield of methyl mercaptan and the productivity per unit time compared to the prior art. As far as temperature and pressure conditions are concerned, these are similar to normal techniques, with temperatures particularly between 250 and 350
°C, preferably 270-300 °C, and the preferred pressure is 12-50 bar, more preferably about 25-35 bar.
It's a crowbar. The invention can be carried out with all known catalysts, especially tungsten sulphide or rhenium sulphide on an activated aluminum support. These preferred catalysts can be prepared in known manner by sulfurizing the oxide or the corresponding alkali salt with hydrogen sulfide. Approximately 450℃ in the presence of air prior to sulfurization
It is advantageous to fire at When the tungsten sulfide obtained from the alkali tungstate salt is used according to the invention by itself without other heavy metal sulfides, it produces almost no methane, whereas in the prior art it was only a promoter. It would be interesting to provide improved conversion without formation. An essential feature of the process of the invention to achieve the object of the invention is the circulation of unconsumed reactants after an initial passage through the reactants, taking care to remove the water formed and the methyl mercaptan already formed. It is to do. This can be carried out by known techniques, namely drying or fractionation of the gas through molecular sieves. By such measures it is possible to avoid employing very low flow rates, which are necessary when trying to avoid inhibition of the reaction by the water formed. The improved technique of the present invention makes it possible to carry out the reaction starting from carbon dioxide and with significantly higher volumetric flow rates than those of the conventional technique, even taking into account circulation. In fact, taking carbon monoxide as an example, the reaction process is expressed by the following formula. CO+H ₂ S→COS+H ₂ ...(1) COS+3H ₂ →CH ₃ SH+H ₂ O ...(2) In the presence of a redox catalyst required for the entire reaction, the reaction system is reduced by the reaction between gas and water. Water is rapidly removed from the CO + H ₂ OCO ₂ + H ₂ ...(3) If carbon dioxide cannot be converted to methyl mercaptan using carbonyl sulfide as a relay, the production of methyl mercaptan from carbon monoxide and the production of carbon dioxide will have the same selectivity. It turns out that there is. In this case, water is completely removed from the reactor. However, contrary to the hypothesis put forward by the authors of the prior literature, carbon dioxide can react rapidly in the presence of hydrogen sulfide to form carbonyl sulfide and water according to the equation: CO ₂ + H ₂ S → COS + H ₂ O (4) The production rate of carbonyl sulfide is about four times higher when starting from carbon dioxide than when starting from carbon monoxide. However, in parallel to this reaction, carbon dioxide is converted at a very slow rate to carbon monoxide and water by the reversible reaction described below. CO ₂ + H ₂ CO + H ₂ O (3') That is, carbon monoxide is an inevitable by-product of the reaction with carbon dioxide, hydrogen sulfide, and hydrogen. We should therefore avoid reaction groups that produce water as a by-product, which inhibits reaction (4) for the production of carbonyl sulfide. For this reason, by removing the water of reaction, carbon dioxide, carbonyl sulfide and carbon monoxide are rapidly converted to methyl mercaptan without inhibiting the reaction in which carbonyl sulfide is formed. The combined result of these factors is that methyl mercaptan can be produced from carbon dioxide, hydrogen sulfide and hydrogen with productivity compatible with industrial requirements. The invention is illustrated by the following non-limiting examples. Example 1 Production of Catalyst Catalyst A was produced by dissolving 71.1 g of tungsten oxide in 1.5 g of an 84% KOH aqueous solution of 41 g of KOH. This solution was rapidly added to 900 g of activated aluminum, evaporated to dryness, and dried at 150° C. for 15 hours. A catalyst with a stoichiometric amount of potassium tungstate supported on activated aluminum was obtained. 36.0g ammonium perrhenate NH ₄ ReO ₄
Catalyst B was prepared by dissolving 1.5 parts of water in 1.5 parts of water. This solution was added to 970 g of activated aluminum. It was evaporated to dryness under atmospheric pressure and dried at 150°C for 48 hours. A catalyst with 3.25% rhenium oxide supported on activated aluminum was obtained. Catalyst B can also be prepared by sulfiding rhenium salts such as ammonium thiorenate, thio salts or other compounds on supports such as aluminum, diatomaceous earth or activated carbon. Catalyst C can also be prepared as described in Belgian Patent No. 874616 (catalyst "HARSHAW" Ni0301T treated with 5% by weight of cesium hydroxide). The reaction was carried out in a cylindrical stainless steel reactor with a length of 45 cm and a diameter of 2 cm. 83.5 g corresponding to 0.1 of each catalyst was charged to the reactor. Before starting the reaction, each catalyst was sulfided with hydrogen sulfide at 370° C. for 5 hours. The reactants CO/H ₂ S/H ₂ were then mixed in the reactor in a ratio of 1/4/4 and heated to 270 °C before being introduced into the tubular reactor filled with catalyst.
was introduced into the reactor after preheating under a pressure of 30 bar. The temperature in the reactor was maintained at 295°C. The gas flow rate, expressed in carbon monoxide, is 50 carbon monoxide per hour per catalyst. The mixture leaving the reactor was expanded to normal pressure via a pressure regulator and analyzed by gas phase gas chromatography. The results after a single pass through the reactor were expressed as both the percentage of carbon monoxide changed and the selectivity of the various products to carbon monoxide changed. The conversion and selectivity defined below under the same reaction conditions for each of the three catalysts A, B and C are shown in Table 1 below. From this Table 1, the selectivity of methyl mercaptan is the highest for catalyst A, with only very small amounts of by-products such as methane and dimethyl carbon sulfide (DMS) being detected.

[Table] The results in Table 1 are clearly superior to the conventional flow rate of 50 h ^-1 . (U.S. Patent No. 4410731, No. 3
(Compare column 1, Table 1, step 6). Example 2 Using a reaction mixture CO ₂ , H ₂ S, H ₂ in the ratio 1/4/4, per liter of catalyst per typical time.
Three catalysts A, B and C at 54 flow rates of _CO2
The reaction was carried out. Keep the preheating temperature at 270℃ and reduce the catalytic reaction temperature.
It was maintained at 295°C. Results are calculated as conversion rate per pass of _CO2 and _CO2
Table 2 below shows the selectivity of various products for

[Table] In the case of this reaction (CO ₂ , H ₂ S, H ₂ ), catalysts A and B gave better results than the conventional catalyst C. Particularly with catalyst A, no formation of troublesome by-products was observed. Example 3 The procedure of Example 2 was repeated with the gas leaving the reactor being recycled. The gas introduction rate into the reactor was kept at 54 _CO2 per catalyst per hour and the _CO2 / _H2S / _H2 ratio was kept at 1/4/4. After removing the methyl mercaptan by fractionation and after passing the gas leaving the reactor through a molecular sieve to remove residual water, the flow rate of the gas in the reactor was regulated by a heated circulation pump. As a result, the water content in the gas was 0.1% or less. The flow rate of gas supplied by the circulation pump is
It was equal to 1760 of _CO2 per catalyst per hour. Table 3 below shows the results obtained with gas circulation. As already mentioned above, the definitions of the terms "conversion rate" and "selectivity" are given at the end of this third embodiment.

[Table] That is, when the method of the present invention is carried out using catalyst A, the amount of methyl mercaptan produced per unit time is 54 x 0.86 x 0.82 = 38. On the other hand, the best results (last two rows) shown in Table 5 of US Pat. No. 4,410,731 are as follows: 5 x 0.52 = 2.6 and 60 x 0.24 = 14.4 It is clear from this that the resulting improvement of the present invention is significant. That is, the superior results of the present invention are achieved by reducing the amount of water in the gas passing through the reactor and by injecting dry recycle gas at high flow rates. Note that in the US technical literature, the term "conversion rate" is used in France by the term "yield," i.e., the number of moles of CO or CO ₂ actually converted to methyl mercaptan per 100 moles of the original. Show the number. In France, on the other hand, the term "conversion" means the mole percent consumed in the reaction of methyl mercaptan and secondary product formation. The percentage that gives only mercaptans is called selectivity. Therefore, yield = conversion rate x selectivity (France) Yield = conversion rate of methyl mercaptan (USA). The difference between the two calculations is shown in the conventional literature and Example 3.

Claims (1)

[Claims] 1. A method of producing methyl mercaptan by heating a gas consisting of carbon monoxide and/or carbon dioxide, hydrogen sulfide and hydrogen in contact with a catalyst based on heavy metal sulfides, and circulating the unreacted gas fraction. In the manufacturing method, water contained in the gas to be circulated is removed,
A method for producing methyl mercaptan, which comprises then bringing it into contact with the catalyst. 2. Methyl mercaptan according to claim 1, wherein the gas circulation is carried out at a volume flow rate of about 50 to 2000, more preferably 500 to 1800, of carbon monoxide and/or carbon dioxide per liter of catalyst space per hour. manufacturing method. 3 In the gas mixture used, the molar ratio of the components carbon monoxide and/or carbon dioxide/hydrogen sulfide/hydrogen ranges from 1/3/3 to 1/4/6, preferably substantially 1/4. /4. The method for producing methyl mercaptan according to claim 1 or 2. 4. Claim 1, wherein the catalyst is a catalyst that uses activated aluminum as a carrier and contains only tungsten sulfide and no other heavy metal sulfides,
The method for producing methyl mercaptan according to item 2 or 3. 5. An alkali metal tungstate in which tungsten sulfide is supported on activated aluminum is calcined in air, preferably at about 450° C., prior to sulfurization;
The method for producing methyl mercaptan according to claim 4, which is produced by subsequently sulfiding with hydrogen sulfide. 6. The catalyst is prepared by sulfiding a salt, thio salt or other compound of rhenium, especially ammonium perrhenate or ammonium thionate, preferably supported on aluminum, diatomaceous earth or activated carbon, in an atmosphere of hydrogen sulfide. Claims 1 and 2 are rhenium sulfide.
The method for producing methyl mercaptan according to item 1 or 3. 7. After separating the methyl mercaptan from the gas passed over the catalyst, it is dried before further contact with the catalyst, as claimed in claims 1, 2, and 3.
The method for producing methyl mercaptan according to item 4, item 5, or item 6. 8. The method for producing methyl mercaptan according to claim 7, wherein the drying is carried out by passing the gas through a molecular sieve.